244 C. W. Andrews — JEpyornk from Madagascar. 



costal element enclosing a canal. On the other hand, there is 

 a median hypapophysis, and hyperapophyses are wanting. The 

 atlas of Casuarins also shows some points of similarity. 



In the axis the preaxial surface of the centrum is concave from 

 ahove downward, about three times as wide as high, and imperfectly 

 divided into two facets, corresponding to the posterior articular 

 surface of the atlas. The postaxial surface is of the usual saddle 

 shape, and much higher than wide ; it presents somewhat the 

 appearance of two crescents joined back to back, and both its dorsal 

 and ventral borders are deeply concave. The ventral surface of the 

 centrum as far back as the hinder border of the parapophyses is very 

 broad : behind this it becomes laterally compressed, and bears 

 a low hypapophysial keel which extends nearly to its hinder edge. 

 On the broad anterior portion a little behind its anterior margin 

 there is a well-marked transverse ridge extending up on to the 

 fused rib. 



The odontoid process is short and broad : on its ventral side, 

 separating its proper articular surface from the upward continuation 

 on to its base of the anterior surface of the centrum, there is 

 a shallow pit for the insertion of a ligament. 



The neural arch is a very massive structure, of which the 

 pedicels are very short and broad. The upper border of the 

 neural spine slopes upward and backward, in which direction also it 

 thickens, so that posteriorly it is bi'oad and shows traces of the 

 bifid condition met with in the succeeding vertebra; its posterior 

 surface bears a deep pit for ligaments. The anterior zygapophyses 

 are merely small circular facets on the antei'ior border of the arch, 

 from which they scarcely project at all. The posterior ones are 

 very large and look downward and slightly backward; they are 

 surmounted by very large tuberous hyperapophyses. The fused 

 cervical rib enclosing the vertebrarterial canal is greatly expanded 

 at its upper end, and there is a broad interzygapophysial bar and 

 a small interzygapophysial foramen. The inner wall of the verte- 

 brarterial canal bears three large pneumatic foramina, the upper one 

 perforating the arch, the lower the centrum. 



The axis above described differs from that of Striithio in possessing 

 a much more prominent neural spine and hyperapophyses, a shorter 

 centrum, a much smaller hypapophysis, much larger vertebrarterial 

 canals (in Struthio these are very small), and less developed anterior 

 zygapophyses. Moreover, in Struthio the posterior articular surface 

 of the centrum is broader than high. It differs from that of 

 Dromcdus in its rather more prominent neural spine and much 

 smaller hypapophysis, in its larger vertebrarterial canal, and in 

 the presence of an interzygapophysial foramen ; from that of Ithea 

 in its much smaller hypapophysis and larger vertebrarterial canal, 

 the form of the neural arch being very similar in the two birds ; from 

 that of Dinornis in its much smaller hj'papophysis, the form of its 

 posterior articular surface, the shape of the odontoid process and 

 its articular surfaces, and in the rudimentary condition of its 

 anterior zygapophyses. 



